Only One Group Invited

Although there are several age groups at my kids’ preschool class, I am only inviting his age group to the party to keep the party size manageable. Outside of mailing the invitations to the kids’ homes, what wording should be used to make this clear? I am trying to avoid parents discussing the party with parents who’s kids were not invited?

The best bet is to be both polite and open.

State, “Please note that only fellow 3 year olds from ___’s class have been invited. Thanks in advance for taking note.”

It may still come up in conversations between parents who received an invitation for their kids and those who did not, but you have done your absolute best by mailing them to their homes and placing this note in the invitation itself as well.